The present invention relates to the generation of shock waves by means of a spark and to be used for the contactless destruction of concrements present in the body of a living being.
U.S. Pat. No. 3,942,531 discloses a device for the destruction and breaking up of concrements situated in the body of a livng being, and in particular this patent discloses a focusing chamber in cooperation with a spark and shock wave generator. The focusing chamber provides specifically for the focusing of the shock wave that issues from a spark. The focusing chamber is basically configured as far as geometry is concerned as a rotational ellipsoid having two focal points. The spark and therefore the shock wave is generated in one of these points. If the electric discharge resulting in this spark is carried out under water and is in fact highly concentrated in that one of the focal points of the ellipsoid, one can in fact generate a highly concentrated shock wave in the second focal point of the ellipsoid. In other words, near pointlike focusing is indeed made possible by means of the rotational-ellipsoidal focusing chamber. The amplitude attainable in the second focal point is in excess of 1 kilobar, and a pulse will have a duration less than one microsecond. This then permits the breaking up and destruction of concrements within the body of a living being, the concrement being situated in that second focal point. Indeed such a concrement can be broken up into smaller pieces which can then be extracted or discharged otherwise.
The known equipment includes two electrodes facing each other in the first mentioned focal point of the ellipsoid, but requiring separate electrical conductors. In order to attain a suitably strong shock wave, voltages between 15 and 30 killovolts are necessary. The effective destruction of such a concrement depends essentially on a very steep flank or leading edge of the shock wave pulse produced, and of course on the duration of that pulse. Generally speaking, one can say that the underwater spark generator requires a very high mechanical strength and very particular and critical electrical properties; the design criteria must be met with a very high degree of accuracy.
German Patent 2,635,635 discloses a spark generator for the generation of shock waves for the contact-less destruction of concrements in living beings, whereby specifically the conductors to and from the electrodes have a low inductivity for better control of the timing of the spark to be generated. The electrodes extend from a holder, and one of the electrodes is extended and looped back so that the electrodes face each other axially. This spark gap as such is exchangeable and placed laterally in the reflector. Thus the electrodes are not coaxially arranged on the large axis of the reflector, which means that the overall rotational symmetry as provided by the chamber is interferred with. This in turn means that a certain interference occurs in the regular propagation pattern of the shock waves so that a certain asymmetry can occur in the focusing. The same is true if one of the outer conductors is constructed as a cage upon which is affixed a second electrode.
The U.S. Pat. No. 3,970,076 discloses a device for the generation of shock waves by means of a spark in the main apex of a reflector. Again, however, the electrodes are not placed coaxial to the large or long axis of the reflecting system.